1 files changed, 105 insertions, 39 deletions

diff --git a/src/dbpage.c b/src/dbpage.c
index 73c31f0da..4e2addad9 100644
--- a/src/dbpage.c
+++ b/src/dbpage.c
@@ -28,7 +28,13 @@
 **
 ** The data field of sqlite_dbpage table can be updated.  The new
 ** value must be a BLOB which is the correct page size, otherwise the
-** update fails.  Rows may not be deleted or inserted.
+** update fails.  INSERT operations also work, and operate as if they
+** where REPLACE.  The size of the database can be extended by INSERT-ing
+** new pages on the end.
+**
+** Rows may not be deleted.  However, doing an INSERT to page number N
+** with NULL page data causes the N-th page and all subsequent pages to be
+** deleted and the database to be truncated.
 */
 
 #include "sqliteInt.h"   /* Requires access to internal data structures */
@@ -51,6 +57,8 @@ struct DbpageCursor {
 struct DbpageTable {
   sqlite3_vtab base;              /* Base class.  Must be first */
   sqlite3 *db;                    /* The database */
+  int iDbTrunc;                   /* Database to truncate */
+  Pgno pgnoTrunc;                 /* Size to truncate to */
 };
 
 /* Columns */
@@ -59,7 +67,6 @@ struct DbpageTable {
 #define DBPAGE_COLUMN_SCHEMA  2
 
 
-
 /*
 ** Connect to or create a dbpagevfs virtual table.
 */
@@ -220,7 +227,7 @@ static int dbpageEof(sqlite3_vtab_cursor *pCursor){
 ** idxStr is not used
 */
 static int dbpageFilter(
-  sqlite3_vtab_cursor *pCursor, 
+  sqlite3_vtab_cursor *pCursor,
   int idxNum, const char *idxStr,
   int argc, sqlite3_value **argv
 ){
@@ -230,10 +237,11 @@ static int dbpageFilter(
   sqlite3 *db = pTab->db;
   Btree *pBt;
 
-  (void)idxStr;
-  
+  UNUSED_PARAMETER(idxStr);
+  UNUSED_PARAMETER(argc);
+
   /* Default setting is no rows of result */
-  pCsr->pgno = 1; 
+  pCsr->pgno = 1;
   pCsr->mxPgno = 0;
 
   if( idxNum & 2 ){
@@ -268,8 +276,8 @@ static int dbpageFilter(
 }
 
 static int dbpageColumn(
-  sqlite3_vtab_cursor *pCursor, 
-  sqlite3_context *ctx, 
+  sqlite3_vtab_cursor *pCursor,
+  sqlite3_context *ctx,
   int i
 ){
   DbpageCursor *pCsr = (DbpageCursor *)pCursor;
@@ -310,6 +318,24 @@ static int dbpageRowid(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
   return SQLITE_OK;
 }
 
+/* 
+** Open write transactions. Since we do not know in advance which database
+** files will be written by the sqlite_dbpage virtual table, start a write
+** transaction on them all.
+**
+** Return SQLITE_OK if successful, or an SQLite error code otherwise.
+*/
+static int dbpageBeginTrans(DbpageTable *pTab){
+  sqlite3 *db = pTab->db;
+  int rc = SQLITE_OK;
+  int i;
+  for(i=0; rc==SQLITE_OK && i<db->nDb; i++){
+    Btree *pBt = db->aDb[i].pBt;
+    if( pBt ) rc = sqlite3BtreeBeginTrans(pBt, 1, 0);
+  }
+  return rc;
+}
+
 static int dbpageUpdate(
   sqlite3_vtab *pVtab,
   int argc,
@@ -321,11 +347,11 @@ static int dbpageUpdate(
   DbPage *pDbPage = 0;
   int rc = SQLITE_OK;
   char *zErr = 0;
-  const char *zSchema;
   int iDb;
   Btree *pBt;
   Pager *pPager;
   int szPage;
+  int isInsert;
 
   (void)pRowid;
   if( pTab->db->flags & SQLITE_Defensive ){
@@ -336,21 +362,29 @@ static int dbpageUpdate(
     zErr = "cannot delete";
     goto update_fail;
   }
-  pgno = sqlite3_value_int(argv[0]);
-  if( sqlite3_value_type(argv[0])==SQLITE_NULL
-   || (Pgno)sqlite3_value_int(argv[1])!=pgno
-  ){
-    zErr = "cannot insert";
-    goto update_fail;
+  if( sqlite3_value_type(argv[0])==SQLITE_NULL ){
+    pgno = (Pgno)sqlite3_value_int(argv[2]);
+    isInsert = 1;
+  }else{
+    pgno = sqlite3_value_int(argv[0]);
+    if( (Pgno)sqlite3_value_int(argv[1])!=pgno ){
+      zErr = "cannot insert";
+      goto update_fail;
+    }
+    isInsert = 0;
   }
-  zSchema = (const char*)sqlite3_value_text(argv[4]);
-  iDb = ALWAYS(zSchema) ? sqlite3FindDbName(pTab->db, zSchema) : -1;
-  if( NEVER(iDb<0) ){
-    zErr = "no such schema";
-    goto update_fail;
+  if( sqlite3_value_type(argv[4])==SQLITE_NULL ){
+    iDb = 0;
+  }else{
+    const char *zSchema = (const char*)sqlite3_value_text(argv[4]);
+    iDb = sqlite3FindDbName(pTab->db, zSchema);
+    if( iDb<0 ){
+      zErr = "no such schema";
+      goto update_fail;
+    }
   }
   pBt = pTab->db->aDb[iDb].pBt;
-  if( NEVER(pgno<1) || NEVER(pBt==0) || NEVER(pgno>sqlite3BtreeLastPage(pBt)) ){
+  if( pgno<1 || NEVER(pBt==0) ){
     zErr = "bad page number";
     goto update_fail;
   }
@@ -358,51 +392,83 @@ static int dbpageUpdate(
   if( sqlite3_value_type(argv[3])!=SQLITE_BLOB 
    || sqlite3_value_bytes(argv[3])!=szPage
   ){
-    zErr = "bad page value";
+    if( sqlite3_value_type(argv[3])==SQLITE_NULL && isInsert && pgno>1 ){
+      /* "INSERT INTO dbpage($PGNO,NULL)" causes page number $PGNO and
+      ** all subsequent pages to be deleted. */
+      pTab->iDbTrunc = iDb;
+      pTab->pgnoTrunc = pgno-1;
+      pgno = 1;
+    }else{
+      zErr = "bad page value";
+      goto update_fail;
+    }
+  }
+
+  if( dbpageBeginTrans(pTab)!=SQLITE_OK ){
+    zErr = "failed to open transaction";
     goto update_fail;
   }
+
   pPager = sqlite3BtreePager(pBt);
   rc = sqlite3PagerGet(pPager, pgno, (DbPage**)&pDbPage, 0);
   if( rc==SQLITE_OK ){
     const void *pData = sqlite3_value_blob(argv[3]);
-    assert( pData!=0 || pTab->db->mallocFailed );
-    if( pData
-     && (rc = sqlite3PagerWrite(pDbPage))==SQLITE_OK
-    ){
-      memcpy(sqlite3PagerGetData(pDbPage), pData, szPage);
+    if( (rc = sqlite3PagerWrite(pDbPage))==SQLITE_OK && pData ){
+      unsigned char *aPage = sqlite3PagerGetData(pDbPage);
+      memcpy(aPage, pData, szPage);
+      pTab->pgnoTrunc = 0;
     }
+  }else{
+    pTab->pgnoTrunc = 0;
   }
   sqlite3PagerUnref(pDbPage);
   return rc;
 
 update_fail:
+  pTab->pgnoTrunc = 0;
   sqlite3_free(pVtab->zErrMsg);
   pVtab->zErrMsg = sqlite3_mprintf("%s", zErr);
   return SQLITE_ERROR;
 }
 
-/* Since we do not know in advance which database files will be
-** written by the sqlite_dbpage virtual table, start a write transaction
-** on them all.
-*/
 static int dbpageBegin(sqlite3_vtab *pVtab){
   DbpageTable *pTab = (DbpageTable *)pVtab;
-  sqlite3 *db = pTab->db;
-  int i;
-  for(i=0; i<db->nDb; i++){
-    Btree *pBt = db->aDb[i].pBt;
-    if( pBt ) (void)sqlite3BtreeBeginTrans(pBt, 1, 0);
+  pTab->pgnoTrunc = 0;
+  return SQLITE_OK;
+}
+
+/* Invoke sqlite3PagerTruncate() as necessary, just prior to COMMIT
+*/
+static int dbpageSync(sqlite3_vtab *pVtab){
+  DbpageTable *pTab = (DbpageTable *)pVtab;
+  if( pTab->pgnoTrunc>0 ){
+    Btree *pBt = pTab->db->aDb[pTab->iDbTrunc].pBt;
+    Pager *pPager = sqlite3BtreePager(pBt);
+    sqlite3BtreeEnter(pBt);
+    if( pTab->pgnoTrunc<sqlite3BtreeLastPage(pBt) ){
+      sqlite3PagerTruncateImage(pPager, pTab->pgnoTrunc);
+    }
+    sqlite3BtreeLeave(pBt);
   }
+  pTab->pgnoTrunc = 0;
   return SQLITE_OK;
 }
 
+/* Cancel any pending truncate.
+*/
+static int dbpageRollbackTo(sqlite3_vtab *pVtab, int notUsed1){
+  DbpageTable *pTab = (DbpageTable *)pVtab;
+  pTab->pgnoTrunc = 0;
+  (void)notUsed1;
+  return SQLITE_OK;
+}
 
 /*
 ** Invoke this routine to register the "dbpage" virtual table module
 */
 int sqlite3DbpageRegister(sqlite3 *db){
   static sqlite3_module dbpage_module = {
-    0,                            /* iVersion */
+    2,                            /* iVersion */
     dbpageConnect,                /* xCreate */
     dbpageConnect,                /* xConnect */
     dbpageBestIndex,              /* xBestIndex */
@@ -417,14 +483,14 @@ int sqlite3DbpageRegister(sqlite3 *db){
     dbpageRowid,                  /* xRowid - read data */
     dbpageUpdate,                 /* xUpdate */
     dbpageBegin,                  /* xBegin */
-    0,                            /* xSync */
+    dbpageSync,                   /* xSync */
     0,                            /* xCommit */
     0,                            /* xRollback */
     0,                            /* xFindMethod */
     0,                            /* xRename */
     0,                            /* xSavepoint */
     0,                            /* xRelease */
-    0,                            /* xRollbackTo */
+    dbpageRollbackTo,             /* xRollbackTo */
     0,                            /* xShadowName */
     0                             /* xIntegrity */
   };